There is a growing interest in small optofluidic (microfluidic) dye lasers. Microfluidic dye lasers can provide laser light for an optical system on a chip (“SOC”) or otherwise function as a compact laser light source. Generally the working fluid is a fluidic dye specifically designed for laser applications. Microfluidic lasers are typically powered by a conventional laser, such as a frequency doubled Nd:YAG pulsed laser or a high power laser diode. The wavelength of the pump light is generally selected such that a given dye can effectively absorb energy from the pump light source. Once excited by a suitable pump light source, the microfluidic dye laser provides laser light at a specific wavelength determined by the laser cavity and the type and concentration of the dye used.
On-chip liquid dye lasers represent promising coherent light sources for ‘lab-on-a-chip’ systems in that they allow the integration of laser sources with other microfluidic and optical devices. On-chip liquid dye lasers are examples of the new class of emerging optofluidic devices, in which the integration of microfluidics with the adaptive nature of liquids enables unique performance that is generally not obtainable within solid state materials. Tunable output wavelengths have been obtained using methods such as varying the dye concentration or by index of refraction tuning methods. Several groups have so far demonstrated such dye lasers by using different materials and laser cavity designs. Research groups at the Department of Micro and Nanotechnology at the Technical University of Denmark, the Department of Chemistry at Harvard and MIT, and the Laboratory of Photonics and Nanostructures in France, have previously reported operable microfluidic lasers using three different approaches.
In “Microfluidic Single-Mode Laser Casing High-Order Bragg Grating And Antiguiding Segments”, Optics Express, Optical Society of America (“OSA”), Jan. 10, 2005, S. Balslev and A. Kristensen (Denmark) described single-mode lasing using a long-period, high-order asymmetric grating. Lasing in all but the fundamental transverse mode in the resonator waveguide was eliminated by inflicting losses on higher modes with the use of antiguiding segments. The microfluidic channel created between glass substrates was 15 mm long and 2 mm wide at the fluid input for the dye, narrowing down to 1 mm at the laser region. The size of the Balslev and Kristensen microfluidic laser was reported to be 10 mm by 20 mm and 1 mm high.
“A Low-threshold, High-efficiency Microfluidic Waveguide Laser”, Journal of the American Chemical Society (“JACS”) Communications, Jun. 3, 2005, also PCT patent application, WO 2006/086551, by Vezenov, et. al. (Harvard/MIT), described the use of a liquid-liquid (L2) waveguide as the basis of a dye laser suitable for integration with microfluidic systems. The Vezenov microfluidic laser was fabricated using soft lithography. A 5-20 mm long active region was terminated at both ends with T-junctions, which were coated with thin layers of gold to act as mirrors for the optical cavity. The height and width of a center channel were reported to be 100 μm×400 μm.
“Microfluidic tunable dye laser with integrated mixer and ring resonator”, Applied Physics Letters, Jun. 22, 2005, Galas, et. al. (France) described a dye laser on a chip using a planar optics for both a polymer resonator and an output waveguide. The Galas laser was based on a ring resonator connected to a waveguide. Laser wavelength was controlled by dye concentration. The device was reported to be 5 mm×5 mm in physical size.
A number of problems in the above microfluidic lasers have been observed. For example, because of the lack of both transverse mode and longitudinal mode selection, there can be undesired simultaneous multiple modes of operation and wide emission line widths. Another problem is that microfluidic laser wavelength tuning has been limited to dye selection and dye concentration, which require relatively complex fluidics apparatus, including valves for porting various types of dye solutions and for varying the dye concentration and index of refraction methods related to the selection of fabrication materials.
There is a need for a microfluidic laser optical structure that can provide both transverse mode and longitudinal mode selection. There is also a need for a tuning method and apparatus to vary the wavelength of a microfluidic laser independently of the type, concentration of the fluidic dye, and fabrication materials.